Acid Base Concepts Flashcards
Equation for acid base homeostasis:
See image
Henderson equation:
H+ =
24 x pCO2/ [HCO3-]
Daily acid produciton =
pH ~ 7 = how many mmol?
How is acid/base homeostatis maintained?
~20,000 mmol acid
pH~7 = 140 nmol
buffering
HCO3- is absorbed where and how?
in the Proximal tubule via carbonic anhydrase
where is H+ excreated?
In the Collecting duct
Components of arterial blood gas:
Components that make up basic chemistry:
pCO2 and pH
HCO3-, Na+, Cl-
Your patient has Primary respiratory acidosis… What must his pCO2 be?
primary respiratoyr acidosis have pCO2 > 40mmHg
Your pt has primary respiratory alkalosis… what does the pCO2 need to be?
pCO2 < 40mmHg
Patient has primary metabolic acidosis, what must the HCO3- be?
HCO3- < 24mmol/L in primary metabolic acidosis
Pt has primary metabolic alkalosis, what must our HCO3- value be?
HCO3- in primary metabolic alkalosis >24 mmol/L
What two things could lead to acidosis?
Primary respiratory: CO2 > 40mmHg
Primary metabolic: HCO3-
What two situations would cause alkalosis?
Primary respiratory: pCO2 < 40mmHg
Primary metabolic HCO3- >24 mmol/L
Four steps for systematic approach to determine acid/base disturbances
- pH (7.40 is normal)
- Determine primary disorder
–metabolic or respiratory
- Calculate expected compensation
- Calculate anion gap
What is meant by expected compenstation? Why is it important?
the body’s ability to appropriately compensate to primary acidosis or alkalosis.
If body cannot completely compensate, this is indicative of secondary disorder.
What equation do we use for compensation in the case of metabolic acidosis (when HCO3- is <24 mmol/L)?
-pCO2 = 1.5 x [HCO3-] + 8
or
-pCO2 = last 2 digits of pH (only down to pH of 7.2)
What equation do we use to calculate compensation for metabolic alkalosis (HCO3- >24 mmol/L)?
pCO2 compensates in same direction as:
bicarb change
Calculation used for Respiratory Acidosis (PaCO2 > 40)
Acute:
Chronic:
Acute: bicarb increase 1 mmol/L per 10 mmHg increase of PaCO2
Chronic: bicarb increases 4 mmol/L per 10 mmHg PaCO2
What are the calculations for compensation in respiratory Alkalosis (PaCO2 <40 mmHg)
Acute:
Chronic
– Acute: bicarb DEcreases 2 mmol/L per 10mmHg PaCO2
– Chronic: bicarb DEcreases 4 mmol/L per 10 mmHg PaCO2
If your patient has a pCO2 = 60 mmHg and is acidotic, what is our primary disorder?
What is the acute and chronic compensation of the bicarb (HCO3-)?
Respiratory acidosis
pCO2 = 60 mmHg (normal is 40 mmHg) thus increase of 20mmHg
HCO3- increase by 2 mmol/L (acute) and 8 mmol/L (chronic)
[Acute: bicarb increase 1 mmol/L per 10 mmHg PaCO2
– Chronic: bicarb increase 4 mmol/L per 10 mmHg PaCO2]
Your patient is acidotic with a bicarb = 15 mmol/L
What is the primary disorder?
What will the expected compensation be?
Metabolic acidosis
pCO2 = (1.5 x 15) + 8 = 30 mmHg
What cations and anions are taken into account when calculating the anion gap?
Na+ cation
HCO3- and Cl- = anions
65 yo with history of ileus presented to surgical team.
NG placed to suction and next am had seizure.
pH = 7.63 pCO2 = 55 sO2 = 94 %
Na+ = 128 K+ = 2.9
Cl-= 70 HCO3- = 50
- What is our primary disorder?
Patient is alkalemic, pCO2= 55 and HCO3- = 50
Primary metabolic alkalosis (HCO3- > 24mmol/L is alkalosis)
65 yo with history of ileus presented to surgical team.
NG placed to suction and next am had seizure.
pH = 7.63 pCO2 = 55 sO2 = 94 %
Na+ = 128 K+ = 2.9
Cl-= 70 HCO3- = 50
Patient has primary metabolic alkalosis. What is the compensation?
with primary metabolic alkalosis, we compensate with pCO2-
Equation: –pCO2 = 0.9 x [HCO3] + 9
-pCO2 = 0.9 x [50] +9 = 54mmHg CO2
(our pts = 55mmHg CO2, thus is appropriately compensated)
65 yo with history of ileus presented to surgical team.
NG placed to suction and next am had seizure.
pH = 7.63 pCO2 = 55 sO2 = 94 %
Na+ = 128 K+ = 2.9
Cl-= 70 HCO3- = 50
Calculate anion gap
[Na+] - [Cl- + HCO3-]
128 - [70 +50} = 8
